Category: Biofeedback

I have a Lightstone, and a copy of the game “Journey to Wild Divine”, despite not being a whifty hippie. My friend Ne0nRa1n gave them to me years ago for biofeedback hacking, but pointed out that the finger sensor connections were broken.

The Lightstone is actually a USB interface to GSR and pulse sensors. Internally, the board uses a M430F133 chip from TI to call the shots, along with a ST72F623F2M1. Why there are two microcontrollers in there, I’m not sure. It could be that one is handling USB communication and the other is dealing with the analog signals, which is supported by the ST part being connected directly to the USB port (with a pair of test points along the traces) and the TI part having a lot of traces running to the analog section of the board.

Overall, the design of the hardware is solid. The Lightstone is easy to open up, the board is well-assembled and has what I’d consider good looking PCB design. There are lots of test points in the analog and digital sections. Spare GPIOs on the MSP430 are broken out to little pads for possible hackery. There are even populated headers that probably were used for programming the microcontrollers.

However, there’s one point where the hardware falls down. The finger contacts for the GSR and pulse sensors are on thin wires with minimal strain relief. Two nice microcontrollers, sweet board design, and it falls apart because wires break.

The sensors are on a 6-pin DIN connector, with red, black, orange, green, yellow, and white wires. The red and black wires each go to a GSR contact. The GSR contacts are silver or silver alloy buttons, so I want to keep those. The other four wires go to the pulse sensor, which is a three pin device. Looking into the front of the device, the left lead gets the yellow wire, the center lead gets the green and orange wires, and the right lead gets the white wire.

To repair the fingertip sensors, I had to pull out the hinge pins that hold the sensor case together. I used very fine-tipped pliers for this, starting from the hinge and then grasping the tip once I had pushed the pin out enough. Then I took the sensors apart, and cut out the bad section of wire. In the image below, the spot to grab the hinge pin is just to the right of the small spring.

I stripped the original cable, and wrapped the stripped sections in heat shrink. I drilled out the molded strain reliefs so I could thread the wires back through them more easily, threaded the wires, and used more heat shrink to improve the strain relief. My new wires are not as flexible as the old ones, but should be more durable. Finally, I soldered the sensors to the ends of the new wires, and put the sensor cases back together.

If you do this repair, be careful soldering to the silver-alloy sensor buttons for the GSR sensor. The silver part is surprisingly easy to soften and distort with heat from a soldering iron. I slightly damaged one of mine, but managed to do the other one with no problems.

I’m using liblightstone to get the information from the device. So far, it seems to be working fine.